Method and apparatus for controlling the transmission power in radio communications system

ABSTRACT

The present invention provides a method for controlling the transmission power requirements in a time division duplex wireless telecommunication system. The method uses the size of the data and Midamble in a burst and the change in rate matching to control the transmission power.

[0001] The present invention relates to a method and apparatus forcontrolling the transmission power in a telecommunications system. Morespecifically, the present invention relates to a method and apparatusfor controlling the transmission power in a Time Division Duplex (TDD)wireless telecommunication system based on a relationship between thesize of the Midamble and the size of the data in a transmission burst.

[0002] It is currently known to perform rate matching in a wirelesstelecommunication system. During this process the rate of the datatransmission in a burst from a base station is matched in order toobtain optimum system performance. The two methods currently used toperform rate matching are repetition and punctuation, both of which arewell known in the field of wireless telecommunications. In order tomaintain the same bit error rate (BER) during rate matching thetransmission (T_(x)) power requirement changes. For example, ifrepetition is used the T_(x) power requirement is reduced, whereas ifpuncturing is used the T_(x) power requirement is increased. Thus whenrate matching is applied the T_(x) power must be adjusted accordingly inorder to maintain a minimum BER and to thereby keep intercellinterference to a minimum.

[0003] It is known within frequency division duplex (FDD) wirelesstelecommunications system to adjust the T_(x) power by 1/RM, where RM isthe rate matching value. As is shown in FIG. 1, this results in a linearrelationship between the T_(x) power requirement represented on the Yaxis of the graph by Δ C/I , and the rate matching value represented onthe X axis of the graph by RM. The initial rate matching value (RM_(O))is equal to one. As can be seen from the graph, if puncturing is usedduring rate matching the T_(x) power requirement increases. Similarly,if repetition is used during rate matching the T_(x) power requirementdecreases.

[0004] Currently there are no provisions for controlling the T_(x) powerin a TDD wireless telecommunication system.

[0005] It is an object of the present invention to provide a method forcontrolling the T_(x) power during the rate matching in a TDD system.Advantageously, by reducing the T_(x) power requirements during ratematching, the overall power requirements of the wirelesstelecommunication system and the system's costs are reduced.

[0006] According to the present invention there is provided a method forcontrolling the transmission power in a time division duplex wirelesstelecommunication system comprising the step of adjusting thetransmission power of the system according to a relationship between thesize of the Midamble signal and the size of the data signal within atransmission burst.

[0007] According to an aspect of the present invention said relationshipbetween the size of the Midamble signal (M) and the size of data signal(D) within said transmission burst is a slope (S).

[0008] According to further aspect the method comprises the furthersteps of determining change in rate matching (ΔRM) used within saidtireless telecommunication system, determining a minimum transmissionpower level required to maintain a predetermined ratio of carrier signalpower to interference signal power, and adjusting said transmissionpower according to said slope and said change in rate matching.

[0009] According to a yet further aspect of the present invention saidpredetermined ratio of carrier signal power to interference signal powerincludes a guard level.

[0010] According to a still further aspect of the invention there isprovided apparatus for controlling the transmission power in a timedivision duplex wireless telecommunication system comprising the stepof:

[0011] adjusting the transmission power of the system according to arelationship between the size of a Midamble signal and the size of adata signal with a transmission burst.

[0012] While the principle advantages and features of the invention havebeen described above, a greater understanding and appreciation of theinvention may be obtained by referring to the drawings and detaileddescription of a preferred embodiment, presented by way of example only,in which;

[0013]FIG. 2 is an example of a burst structure;

[0014]FIG. 3 is a graph which shows the relationship of transmissionpower to rate matching in a TDD system.

[0015]FIG. 4 shows a partial handset architecture in accordance with theinvention; and,

[0016]FIG. 5 shows a partial base station architecture in accordancewith the invention.

[0017] In order to fully understand the present invention, a specificexample will now be given with reference to FIGS. 2 and 3.

[0018]FIG. 2 shows the structure of a typical burst signal 10. The burstsignal consists of two data parts 12 and 14, a Midamble part 16, and aguard period 18. Each data part consists of 976 bits and the Midambleconsists of 512 bits. The guard period consists of N bits, where N is aninteger number. As will be appreciated by the skilled man, the sizes ofthe data parts, Midamble and guard period may vary according to thewireless telecommunication system's particular requirements. It willalso be appreciated that the structure may not contain a guard period.

[0019] According to the present invention the T_(x) power of a mobilephone is changed based on the following factors: a puncturing limitvalue, a minimum carrier signal power to interference signal powerratio, and the amount of data in the burst. The minimum carrier signalpower to interference signal power ratio may include a guard level.

[0020] A maximum T_(x) power is set according to a puncturing limit(PL). The value of PL is set at the maximum amount of puncturing which asignal can withstand. Any puncturing beyond this value results in asignal which has lost too much data to be successfully interpreted. ThePL is determined by the rate matching parameters of thetelecommunication system and is transmitted from the base station touser equipment, such as a mobile phone.

[0021] A minimum T_(x) power is set according to a minimum value of theratio of carrier signal power to interference signal power (C/I min) inwhich the system can still function properly. The value of C/I min maybe predefined based on knowledge of the system or it may be transmittedby the base station and be derived from previous values of C/I min, orbe an estimation. This ratio may include a guard level which functionsto insure that the minimum T_(x) power level is never reached.

[0022] The amount of data in the burst is then compared to the amount ofMidamble bits. As will be appreciated, this value may vary considerablyand each burst must be evaluated individually.

[0023] The amount in which the T_(x) power can be reduced or increasedis then calculated. The maximum amount the T_(x) power can be increasedby is preferably set at the PL value. Increasingly the T_(x) powerbeyond the PL value will not improve the system's performance as theamount of data lost due to the puncturing process determines the pointof system failure. Furthermore, the minimum level to which the T_(x)power can be reduced is preferably set at the C/I min value previouslydiscussed. The C/I min value may include a guard level. Alternatively,the maximum and minimum T_(x) power levels may tend towards an asymptoteat these values. For the region between the maximum and minimum T_(x)power levels, the value of the T_(x) power is calculated according to arelationship between the size of the data and the size of the Midamblein each burst.

[0024]FIG. 3 shows a graph of the specific example of the presentinvention with the X axis representing the value of the rate matching(RM) and the Y axis representing the change in the value of the ratio ofthe carrier signal power to interference signal power (Δ C/I ). As willbe appreciated an increase in T_(x) power will result in an increase inthe power of the carrier signal and thus an increase in the value of ΔC/I.

[0025] For this specific example the value of Δ C/I min is predeterminedand transmitted by the base station. Additionally, the PL value ispredetermined and may also be transmitted by the base station. Themaximum and minimum T_(x) power levels are depicted on the graph in FIG.3 by the solid lines 31 and 32 respectively. In this specific examplethe value of Δ C/I min is equal to 0.5 dB and the, value of PL is equalto 0.5 dB.

[0026] In an enhancement to the specific example shown in FIG. 3 a guardlevel 40 is included. This has the effect of increasing the minimumlevel to which the T_(x) power can be reduced.

[0027] For the region between the PL and the Δ C/I min the rate ofchange of T_(x) power is determined according to the amount of data inthe burst (D) and the size of the Midamble (M). The rate of change isconstant and is shown graphically in FIG. 3 by slope S. The slope iscalculated according to equation 1: $\begin{matrix}{S = \frac{\left( {M - D} \right)}{D}} & {{Equation}\quad 1}\end{matrix}$

[0028] For the burst shown in FIG. 2, where D equals 1952 and M equals512, S equals −0.738. Thus a negative slope will exist provided the datacomponent of the burst is greater than the Midamble component. Aspreviously explained and shown in FIG. 1, in an FDD system where notMidamble exists, the slope equals −1.

[0029] The amount the T_(x) power is increased or decreased can then becalculated according to the following set of rules. The change in T_(x)power is shown graphically in FIG. 3 as Δ C/I and is calculated indecibels (dB).

[0030] The initial value of the rate matching (RM_(O)) is equal to 1.This corresponds to an initial Δ C/I (Δ C/I_(O)) value of 1. The pointof intersection of RM_(O) and Δ C/I _(O) is shown in FIG. 3 by referencenumeral 35. The new value of rate matching is denoted as RM_(N). Whenthe Δ C/I min value is reached, the rate matching at that point isdenoted by RM_(max). As will be appreciated, the rate matching (RM) isconstantly being changed according to the system's requirements. Thechange in rate matching (ΔRM) is measured in decibels and is calculatedaccording to equation 2. $\begin{matrix}{{\Delta \quad {RM}} = {10{\log \left( \frac{{RM}_{N}}{{RM}_{o}} \right)}}} & {{Equation}\quad 2}\end{matrix}$

[0031] The corresponding charge in T_(x) power, shown graphically inFIG. 3 as a change in Δ C/I, is then calculated according to equation 3.$\begin{matrix}{{\Delta \quad {C/{I({dB})}}} = \left\{ \begin{matrix}{{SxPL}({dB})} & {:{{RM} \leq {PL}}} \\{{Sx\Delta}\quad {{RM}({dB})}} & {:{{PL} \vartriangleleft {RM} \leq {RM}_{\max}}} \\{\Delta \quad {C/I}\quad \min} & {:{{RM} \vartriangleright {RM}_{\max}}}\end{matrix} \right.} & {{Equation}\quad 3}\end{matrix}$

[0032] When the rate matching uses puncturing the T_(x) power level willbe increased according to the slope in the portion of the graph betweenRM_(O) and PL. Similarly, when the rate matching uses repetition theT_(x) power level will be reduced according to the slope in the portionof the graph between RM_(O) and RM_(max).

[0033]FIG. 4 shows the relevant features of a handset architecture 40 inaccordance with a first embodiment of the invention. RF signals arecoupled by an antenna 42, which is connected via a duplexer 44 totransmit and receive circuitry 46, 48. The power level of receivedsignals is measured by power level detector 52 after the signals havebeen filtered and demodulated by filter/demodulator 50. The power leveldetector provides data to a microprocessor 54 which compensates for ratematching and provides data to power control 56 which, in turn, providespower control data bits. The power control bits are combined withencoded signals prior to, modulation and subsequent transmission via theantenna.

[0034]FIG. 5 shows how the invention can be implemented in a basestation 70. In the transmit path, after signals have been encoded byencoder 72, the signals are amplified in an amplifier control circuit74. The amplifier control circuit comprises a power control unit 76, asare typically employed in prior art base stations and a spreading andmatching compensation circuit 78. The rate matching and spreadingcompensation then offsets the power control. The burst then goes throughthe ordinary transmission and modulation circuits. The antenna 82. Themodulator would typically contain signal filters.

[0035] As will be appreciated by those skilled in the art, variousmodifications may be made to the embodiment hereinbefore describedwithout departing from the scope of the present invention. For example,the method of adjusting T_(x) power previously described can be applieddue to change in spreading factor. As is well know in FDD type systems,the T_(x) power requirement changes linearly with respect to a change inthe spreading factor. For example, if the spreading factor doubles, theT_(x) power requirement is halved. The formula given in equation 1 tocalculate the T_(x) power adjustment according to the Midamble size canbe used to calculate the T_(x) power adjustment due to the spreadingfactor in a TDD system.

1. A method for controlling the transmission power in a time divisionduplex wireless telecommunication system comprising the step of:adjusting the transmission power of the system according to arelationship between the size of a Midamble signal and the size of adata signal within a transmission burst.
 2. A method according to claim1, wherein said relationship between the size of the Midamble signal (M)and the size of data signal (D) within said transmission burst is aslope (S).
 3. A method according to claim 2, wherein:$S = {\frac{\left( {M - D} \right)}{D}.}$


4. A method according to claims 1-3, wherein the method comprises thefurther steps of: determining a change in rate matching (ΔRM) usedwithin said wireless telecommunication system, determining a puncturing(PL), determining a minimum transmission power level required tomaintain a predetermined ratio of carrier signal power to interferencesignal power (Δ C/I min), and calculating a ratio of carrier signalpower to interference signal power (Δ C/I ). 5.${\Delta \quad {RM}} = {10{\log \left( \frac{{RM}_{N}}{{RM}_{o}} \right)}}$

where: RM_(O)=initial rate matching value, RM_(N)=new rate matchingvalue.
 6. A method according to claims 4 or 5, wherein:${\Delta \quad {C/I}} = \left\{ \begin{matrix}{SxPL} & {:{{RM} \leq {PL}}} \\{{Sx\Delta}\quad {RM}} & {:{{PL} \vartriangleleft {RM} \leq {RM}_{\max}}} \\{\Delta \quad {C/I}\quad \min} & {:{{RM} \vartriangleright {RM}_{\max}}}\end{matrix} \right.$

where: RM_(max)=rate matching value corresponding to Δ C/I min.
 7. Amethod according to claims 4-6, wherein said time division duplexwireless telecommunication system comprises at least one base stationand said Δ C/I min value is transmitted from a base station.
 8. A methodaccording to claims 4-7, wherein said Δ C/I min value includes a guardlevel.
 9. A method according to claims 4-8, wherein said puncturing,limit (PL) is transmitted from said base station.
 10. Apparatus forcontrolling transmission power in a time d vision duplex wirelesstelecommunication system including power control means operable toadjust the transmission power of the system according to a relationshipbetween the size of a Midamble signal and the size of a data signalwithin a transmission burst.
 11. Apparatus according to claim 10,wherein said relationship between the size of the Midamble signal (M)and the size of data signal (D) within said transmission burst is aslope (S).
 12. Apparatus according to claim 11, wherein:$S = {\frac{\left( {M - D} \right)}{D}.}$


13. Apparatus according to claims 10-12, wherein the power control meansis operable to: determine a change in rate matching (ΔRM) used withinsaid wireless telecommunication system; determine a puncturing limit(PL); and, determine a minimum transmission level power required tomaintain a predetermined ratio of carrier signal power to interferencesignal power (Δ C/I min;, whereby to calculate a ratio of carrier signalpower to interference signal power (Δ C/I ).
 14. Apparatus according toclaim 13, wherein a base station of the time division duplex wirelesstelecommunications system is operable to transmit said Δ C/I min value.15. Apparatus according to claims 13 or 14, wherein said Δ C/I min valueincludes a guard level.
 16. Apparatus according to claims 13-15, whereinsaid base station is operable to transmit said puncturing limit (PL).